An approximate solution to the best symmetric Tucker decomposition REF  is the HOEVD [1]} result:
\(\displaystyle \mathbf {Q}_{\text{hoevd}} \in \operatorname{St}(n,r) ~\text{given~by~the~} \text{leading~}r~\text{eigenvectors~of~}\operatorname{mat}({X})\operatorname{mat}({X})^\top .\) 
